1. Field of the Invention
This invention relates to spark plug cable insulators, particularly a spark plug boot having a rigid shell for adding structural strength to an elastomer boot used to protect the connection between a spark plug cable terminal and a spark plug.
2. Description of the Prior Art
Conventional spark plug cables are very flexible in order to permit a mechanic to run spark plug cables from a spark plug to a distributor in a convenient manner. This flexibility, however, results in occasional difficulty for the mechanic who is attempting to seat the spark plug cable terminal onto the spark plug. Particularly, this problem arises when the spark plug is in a somewhat inaccessible area in the engine compartment, or when the spark plug is located within a well of the engine block. The common practice in the art of using an elastomer boot attached to the end of the spark plug cable for covering the spark plug cable terminal and a received spark plug only exasperates the aforementioned problem of installation difficulty. This is because the boot is also flexible and the tight fit between the boot and the spark plug frequently results in a false sensation that a properly seated connection with the spark plug has been achieved, when in fact this is not the case.
An additional problem arises with conventional spark plug cable systems, in that removal of the spark plug cable from the spark plug is frequently difficult. This is because the elastomer boot tends to seal onto the spark plug, creating both suction and adhesion. In situations of limited accessibility, the mechanic frequently chooses to pull on the spark plug cable a considerable distance away from the spark plug terminal, causing fatigue to the electrical connections within the spark plug cable.
There have been a number of attempts in the prior art to devise a successful spark plug cable connection system.
One class of spark plug cable connection systems involves spark plug cable terminal protectors where the terminal is bent at an angle of 90.degree. relative to the spark plug.
U.S. Pat. No. 1,245,931 to Lanman, is directed to the problem of a spark plug being subject to injury from falling objects and water short circuiting. Lanman solves this problem by providing an L-shaped metal sheath which clamps to both the spark plug cable and the spark plug.
U.S. Pat. No. 1,376,844 to Weber, is directed to the problem of making good electrical contact between the spark plug and the spark plug cable. Weber solves this problem by providing an L-shaped insulator having at one end the spark plug cable and at the other end an aperture into which the spark plug inserts, thereby making contact with the spark plug cable terminal.
U.S. Pat. No. 2,301,570 to Nowosielski, is directed to the problem of difficulty of making good mechanical and electrical connection of spark plug cables to spark plugs, as is required in aircraft engines. Nowosielski solves this problem by providing an electromagnetic shield, a cover, a wire piercing element, an insulator, and bushing for the spark plug cable to pass through. The bushing coupled with the cover is designed to be permanently attached to the spark plug, and is not independent of the spark plug cable.
U.S. Pat. No. 2,323,399 to Jacobi, is directed to the problem of electromagnetic wave propagation from spark plug terminals. Jacobi solves this problem by using a shield composed of two layers; an inner rubber shield and an outer conductive rubber shield.
U.S. Pat. No. 2,382,805 to Mosthaf, is directed to the problems encountered in aircraft engine operating environments. Mosthaf solves these problems by providing a sheathing of kiln fired ceramic over the spark plug cable and the spark plug upper end.
U.S. Pat. No. 2,686,511 to Platner, is directed to the problem of spark plug terminal shields being blown off during engine operation. Platner solves this problem by providing a cover over the spark plug. A steel shield within the cover has axially positioned therein the spark plug cable which is covered by a ceramic.
U.S. Pat. No. 4,443,047 to Hofmann, is directed to the problem of the spark plug terminal becoming deformed during removal from the spark plug. Hofmann solves this problem by providing a two-piece L-shaped boot covering. The boot covering conforms to the already present shape of the boot and the direction of the spark plug cable and supplies a handhold to aid removal from the spark plug.
A second class of spark plug cable connection systems involves protectors for spark plug cable terminals which are straight (that is, 180.degree.) in relation to the spark plug.
U.S. Pat. No. 2,685,872 to Berstler, is directed to the problem of electrical leakage from spark plugs. Berstler teaches that this can be solved by using a two part insulator surrounding the spark plug components. Specifically, his teachings are directed to an improved type of spark plug, wherein a base insulator is made of a machinable material and an upper insulator is made of a cheaper type of insulator material.
U.S. Pat. No. 3,076,113 to Candelise, is directed to the problem of loss of dielectric effectiveness of the spark plug cable boots over time. Candelise solves this problem by providing, interior to the spark plug itself, the spark plug cable terminal. A protective rubber boot is also provided.
U.S. Pat. No. 3,128,139 to Estes, is directed to the problem of electromagnetic waves emanating from the spark plug. Estes teaches that this problem may be solved by providing a metallic shield over the spark plug cable terminal attachment area.
U.S. Pat. No. 3,803,529 to Rohrig et al, is directed to the problems associated with spark plug terminals in which moisture and conductor kinking can occur. Rohrig et al solve these problems by providing two insulating layers. One is a body and the other is a casing, where both are made of a thermal setting material. An elastomeric material fills in any gaps therebetween. An end portion is made a metal shield.
U.S. Pat. No. 3,914,003 to Loy, is directed to the problem of the interior of the spark plug terminals becoming brittle and deteriorating over time. Loy solves this problem by providing an exterior thermal setting plastic and an interior elastomeric plastic. Loy surrounds the upper extremity of the spark plug with the thermal setting plastic, using the elastomeric plastic to protect only the spark plug cable conductors.
U.S. Pat. No. 4,621,881 to Johansson et al, is directed to the problem of prior art elastomer boots being of a size which causes a tight fit with the spark plug, resulting in difficulty during removal therefrom. Johansson et al solve this problem by providing a stiff material which surrounds an elastomeric material. The elastomeric material extends between the upper end of the spark plug to the beginning of the spark plug cable, but is not co-extensive with the spark plug cable. The outer material combines with the inner material only for sealing purposes.
Devices have been developed to protect electrical connections by means of a shield against both operational and environmental problems.
U.S. Pat. No. 3,845,459 to Normann, is directed to the problem of female sockets suffering from dielectric breakdown and mechanical fatigue from insertion of oversized male connectors. Normann solves this problem by providing a bridged insulator which surrounds the female electrical connector. A suggested material is Teflon.RTM.. This invention, though not specifically directed to spark plug wires, is of interest for showing a rigid dielectric covering over the electrical contact.
U.S. Pat. No. 4,614,392 to Moore, is directed to the problem of protecting an electrical connection from well fluids. Moore solves this problem by providing an elastomer cover which snaps together. The covering has an outer protective skin.
None of the above cited references teach a solution to the spark plug accessibility problems enumerated above. Accordingly, there remains in the art the need to provide a rigid shell for adding structural strength to elastomer boots so as to permit easy accessibility to remotely located spark plugs.